Mobile terminals are gradually developed together with the increase in their amount used, and various functions and services are developed accordingly. A portable terminal such as a mobile terminal or smart phone has a camera to take photographs or moving pictures, and provides a service for storing the taken image or performing video communication. Recently, a camera module has been mounted in most portable terminals. That is, demands on micro-miniature camera modules are rapidly increased.
In a micro-miniature camera module, high resolution is implemented as the number of sheets of lenses increases. A recent camera module has a built-in auto focusing (AF) function of moving a portion of lenses to an optical axis. An AF module is a conventional driving means for moving lenses, and a voice coil motor (VCM) was used as the AF module.
The VCM is a motor developed based on the principle that a diaphragm is vibrated by a force generated between voice current flowing in the coil of a speaker and a magnetic force of a permanent magnet according to the Fleming's left-hand rule. The VCM performs a linear reciprocating motion on a lens at a short distance.